This application claims the priority of Korean Patent Application No. 2002-57394, filed on Sep. 19, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to perpendicular magnetic recording media, and more particularly, to a perpendicular magnetic recording medium with a high thermal stability and a high recording density.
2. Description of the Related Art
A perpendicular magnetic recording method is used in hard disk driver (HDD), which are widely used as data storage devices, to increase the recording density and capacity thereof. In a perpendicular magnetic recording method, a magnetization is oriented perpendicularly to the film plane of a recording medium to increase the recording density of the recording medium. In addition, in order to increase the thermal stability and recording density of perpendicular magnetic recording media, several key features of media should be satisfied such as strong perpendicular magnetic anisotropy energy over 10e6 erg/cc, small average grain size, narrow distribution of grain size and small magnetic domains.
In conventional perpendicular magnetic recording media, as perpendicular magnetic recording anisotropic energy increases, crystal grains or magnetic domains enlarge. Likewise, as crystal grains or magnetic domains diminish, perpendicular magnetic recording anisotropic energy decreases.
FIG. 1 shows the layer structure of a conventional perpendicular magnetic recording medium. FIG. 2 shows the layer structure of a conventional perpendicular magnetic recording medium having a double magnetic layer.
Referring to FIGS. 1 and 2, the two conventional perpendicular magnetic recording media have a perpendicular orientation underlayer 102 and a soft magnetic layer 202 that are placed below perpendicular magnetic recording layers 103 and 203, respectively.
To be more specific, as shown in FIG. 1, the perpendicular orientation underlayer 102 is placed on the upper surface of a substrate 101, and the perpendicular magnetic recording layer 103 is placed on the perpendicular orientation underlayer 102. A protection layer 104 is placed on the perpendicular magnetic recording layer 103 to protect the perpendicular magnetic recording layer 103. Thereafter, a lubricating layer 105 is placed on the protection layer 104 to protect the perpendicular magnetic recording layer 103 and the protection layer 104 against collisions with a data writing/reading head slider and to induce a smooth sliding of the head slider.
Referring to FIG. 2, the conventional perpendicular magnetic recording medium with a double magnetic recording layer has the soft magnetic layer 202 instead of the perpendicular orientation underlayer 102 of FIG. 1. The soft magnetic layer 202 is formed on a substrate 201. The perpendicular magnetic recording layer 203 is placed on the soft magnetic layer 202. A protection layer 204 and a lubricating layer 205 are sequentially formed on the perpendicular magnetic recording layer 203.
Each of the two conventional recording media has a perpendicular magnetic recording layer. The perpendicular magnetic recording layer is formed of a material with a large perpendicular anisotropy energy (Ku) to secure a high thermal stability required upon high-density recording. However, the material with a large perpendicular anisotropy energy provides large crystal grains and large magnetic domains and generates large noise and accordingly is not adequately helpful to achieve high-density recording. Meanwhile, if a material with small crystal grains and small magnetic domains is used, high-density recording can be achieved with an excellent signal-to-noise ratio (SNR), but thermal stability cannot be secured because of its small perpendicular magnetic anisotropic energy (Ku).